Inclinometry with 'Spare' inclinometer on left A-frame

Summary
On 981115 inclinometry was done with the spare inclinometer mounted next to the one on the left A-frame, and plugged into the channels that usually carry data from that on the right A-frame; i.e. we will measure the left A-frame with two meters :

   Datasets          HST start    mean leg temperatures   Humidity
                                  start   middle   end       %
   inc981114 (regular) 11:05       2.4     3.5     4.7      20
   inc981115 (2 lefts) 10:33       2.5     3.9     5.1      40 

The double measurement of the L-A-frame
The raw data from the X- Y- and T-channels are shown below, with S representing the measures from the Spare inclinometer (on the L-A-frame). The scales are all in mV, with 20mV = 1" of tilt and 10mV = 1 deg C of temperature :

The similarity between the measures from the two inclinometers on the L-A-frame is striking. This essentially confirms that the L inclinometer is performing adequately. However, the detailed differences are shown below :

The differences (ripples of up to 1" amplitude on 6" systematics) are not apparently thermal. The data may prove useful in refining (indeed, in activating) the thermal correction algorithms within the inclinometry reduction software.

(Note added 981119)
However, the data may also be used to check if the symmetry of an inclinometry dataset is dependent upon the particular inclinometer in use. To this end the table below shows 'symmetry' measures from some recent data covering periods of both 'good' and 'bad' symmetry. Note :

• the correlation between TY and RY is 'good' because the two are servo-ed together. A plot of one against the other lies along a line of slope unity with rms scatter of about 0.7"
• The phase-shifted, sign-inverted LY is at times well correlated with RY (~1.5) and at other times badly correlated (>2.5).
• Because RY is disabled by the inclusion of SY, we must perform such a comparison via TY, hence the column below showing the LY-TY correlation.
• The last column shows the one SY-TY correlation.

The correlations of LY with either RY or TY are almost identical, so the value of 2.13 on 981115 indicates neither a particularly good nor bad condition. The SY-TY value on that day (1.52) might indicate that the LY data is suspiciously bad, and that the current inclinometer in use on the left A-frame is suspect. Further evidence will be sought.